1 Technical Field
This disclosure relates generally to an engine control system which may be employed in automotive vehicles and is designed to control operations of actuators such as fuel injectors to regulate a combustion state of fuel in an internal combustion engine for achieving a desired level of performance of the engine.
2 Background Art
Japanese Patent First Publication No. 2009-156034 discloses an engine control system which calculates controlled variables or parameters associated with the quantity of fuel to be injected into an internal combustion engine, the injection timing, and the quantity of intake air sucked into the engine so as to meet required engine performance parameters such as the amount of exhaust emissions (e.g., NOx and CO), output torque of the engine, the consumption of fuel in the engine, the level of combustion noise from the engine.
The engine control system compares the level of combustion noise produced when the fuel has been sprayed actually at a reference fuel injection parameter in the condition where the concentration of oxygen in a cylinder of the engine is a certain value with that expected when the fuel is sprayed according to the reference fuel injection parameter in the condition where the concentration of oxygen in the cylinder meets a target value. When a difference between them is greater than a permissible range, the engine control system corrects the reference fuel injection parameter so that the difference may fall in the permissible range and actuates a fuel injector according to the corrected reference fuel injection parameter to optimize the level of the combustion noise (i.e., one of performance parameters, as will be described later). The reference fuel injection parameter, as referred to above, may include the amount of fuel sprayed from a fuel injector in the pilot injection event or the main injection event in a multi-injection system, an injection-to-injection interval, the timing of the main injection event, or a pilot-to-main injection interval.
There may, however, be correlations between the plurality of performance parameters. The decreasing of the pilot-to-main injection interval to reduce the combustion noise (i.e., one of the performance parameters) may, therefore, result in an increase in amount of smoke (i.e., one of the performance parameters) emitted from the engine. Specifically, when the engine control system calculates target values of the performance parameters independently of each other and changes a plurality of controlled parameters for actuators simultaneously for bringing them into agreement with the target values, it may result in interference between the different types of the performance parameters in that when one of the performance parameters reaches its target value, another performance parameter deviates from its target value.
The engine control system may also be designed to use combustion parameters associated with states of combustion of fuel in the engine as intermediate parameters to regulate the controlled parameters so as to bring actual values of the performance parameters into agreement with target values thereof. When a deviation occurs between an actual value of one of the combustion parameters and a target value thereof, it is preferable to minimize such a deviation in a way suitable for instantaneous operating conditions of the engine.